Hi, I'm having a lot of problems with BGA's shorts, we are using 0.005" stencil aperture 1 to 1 (0.014)", the paste is centre (I can not measured the height)was verified using electronic microscopie, the placement is centre (I'm using local fiducials), the profile is 215 peak and around 65sec above 183 grades C. The assembly has 4 BGA's (the same component) located one behind another one and the shorts are random. I appreciate any suggestion or input. thanks

These random shorts, are they most prevailent on the edges, corners, or truly all over the place. It almost sounds like package warp/delamination or something of that nature. Are you baking parts per MSL requirements?

You might wanna try a small reduction in your stencil aperture. For example, for a 30-mil pad go 26-mil square aperture with 8 to 10-mil radius on your corners.

Also, look at your designs. Is there enough resist between your pad and ball?

Another thing that's bitten me in the arse.... excessive HASL on the VIA's which caused top-side gasketing problems at the Top-Side printer. The HASL "icicled" out of the via's due to excessive HASL, and plus the VIA's weren't tented.